A wide variety of plants contain compounds with cyano groups which contribute to the toxicity of the plant material for food or feed use. Some of these compounds, termed cyanogenic glycosides, exert their toxicity by releasing hydrogen cyanide upon acidic or enzymatic hydrolysis. An example of a cyanogenic glycoside is amygdalin, or mandelonitrile beta-gentiobioside, which occurs in Rosaceae seeds including peach, bitter almonds, apricot, apple, cherry, pear, plum and quince. Another common cyanogenic glycoside is linamarin, acetone cyanohydrin beta-D-glucoside, which is sometimes referred to as phaseolunatin. Linamarin occurs in cassava from which tapioca is made, many varieties of lima beans, linseed, white clover and many species of Lotus, all of which are plants eaten by humans or domestic animals. Cyanogenic glycosides have been reported to occur in common edible plants including sorghum, black-eyed pea, garden pea, yam, maize and cashew nuts. There are about twenty known cyanogenic glycosides which occur in plants. In addition to amygdalin and linamarin there is prunasin, dhurrin, vicianin, taxiphyllin, lotaustralin, sambunigrin, acacipitalin, zierin and triglochinin.
Cyanide compounds other than cyanogenic glycosides also occur in plant materials. Lathyrism is a neurological disease that affects animals and humans who eat lathyrus peas, a small drought-resistant high protein legume grown as a food in India. Toxicity in Lathyrus is due to beta-N-(gamma-L-glutamyl) aminopropionitrile. Simmondsin, 2-(cyanomethylene)-3-hydroxy-4,5-dimethoxycyclohexyl-beta-D-glucoside occurs in seeds, hulls, leaves, twigs and roots of jojoba, a plant that is grazed by various animals in the wild in the Southwestern United States.
Jojoba, Simmondsia chinensis, is a bushy plant that grows well in the arid lands of Arizona, California and Mexico where it is being cultivated as a plantation crop. The seeds contain about 50% by weight of an oil which is chemically and physically similar to sperm whale oil, a raw material no longer available in the United States. Jojoba oil has physical characteristics that are of value for certain commercial products.
Jojoba meal is the plant material remaining after jojoba seeds containing some hulls have been commercially pressed and/or solvent extracted to remove jojoba oil. Jojoba seed meal is the material remaining after deoiling completely dehulled seeds. Deoiled jojoba seed meal contains about 30% crude protein and 8% metabolizeable carbohydrate, which make it a potential feed ingredient for livestock. Even the seed hulls contain 7% crude protein and 3% metabolizeable carbohydrate. The problem is that jojoba meal also contains approximately 4.5% simmondsin, 1% simmondsin 2'-ferulate and at least two other minor toxicants that are structurally related to simmondsin. Simmondsin is an antinutritional factor which even at 0.15% levels in a normal ration causes rats to reduce their food intake. Although acute toxicity of simmondsin is very low, repeated daily doses to rodents lead to weight loss and eventual death. The toxicity of simmondsin is related to its cyano functional group, either as part of the simmondsin structure or more likely as a metabolic degradation product. Removal of simmondsin and the related cyanomethylenecyclohexyl glucosides from the meal, or chemical modification of their cyano groups, substantially eliminates meal toxicity.
The cyano group is chemically modified in meals treated with ammoniacal hydrogen peroxide, and the meals can be used as an additive in animal feed. The methods described here detoxify jojoba meal by hydrating the cyano group of simmondsin. In an aqueous solution of pure simmondsin, ammoniacal hydrogen peroxide hydrates the cyano group quickly and quantitatively to an amide.
The hydration of cyano groups to amides with alkaline hydrogen peroxide is known as the Radziszewski reaction. Early investigations of this reaction have shown that hydration of a cyano function to an amide with hydrogen peroxide in base can be 10,000 times faster than with hydroxyl ion alone.
Hydrogen peroxide alone is ineffective in this hydration. Cinnamonitrile and acrylonitrile have been converted to amides by Radziszewski reaction conditions.
The Radziszewski reaction is carried out in solution, usually water, using alkali bases such as sodium hydroxide. Aqueous treatment of jojoba meal leads to an unfilterable mass as the meal absorbs several times its weight of water. Also, base causes hydrolysis of the glycoside linkage of simmondsin resulting in the formation of 2-hydroxy-3-methoxybenzyl cyanide, a compound that is more toxic than simmondsin. Normal Radziszewski reaction conditions are, therefore, undesirable for treating jojoba meal.